The present invention relates to expandable intraluminal vascular devices, generally referred to as stents. More precisely, the present invention is directed to stents that have a metallic cladding for improved expansion characteristics and radiopacity.
Stents are used to maintain patency of vessels in the body, such as a patient's arteries. A variety of delivery systems have been devised that facilitate the placement and deployment of stents. The stent is initially manipulated while in its contracted or unexpanded state, wherein its reduced diameter more readily allows it to be introduced into the body lumen, such as a coronary artery, and maneuvered into the target site where a lesion has been dilated. Once at the target site, the stent is expanded into the vessel wall to allow fluid to flow through the stent, thus performing a scaffolding function. Stents are usually mounted on balloon catheters and advanced to a lesion site by advancing the catheter. At the site, the stent is expanded by inflating the balloon on which the stent is mounted. Deflation of the balloon and removal of the catheter leave the stent implanted in the vessel in an expanded state. It is also possible to dilate a vascular lesion and deploy a stent at the same time using the same expandable member or inflatable balloon. This variation of the procedure described above obviates the need for a separate balloon dilation catheter and stent deployment catheter.
Stents are typically formed from biocompatible metals such as stainless steel, nickel-titanium, tantalum, and the like, to provide sufficient hoop strength to perform the scaffolding function of holding the patient's vessel open. Also, stents have minimal wall thickness in order to minimize blood flow blockage. But stents can sometimes cause complications including thrombosis, and neointimal hyperplasia by inducement of smooth muscle cell proliferation at the site of implantation of the stent. Such stents typically also do not provide for delivery of localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, which can be useful for overcoming such problems.
In the evolution of stents, there have been developments in the field of stents coated with a layer of polymers. The polymeric materials are typically capable of absorbing and releasing therapeutic drugs. Examples of such stents are disclosed in U.S. Pat. No. 5,443,358 to Eury; U.S. Pat. No. 5,632,840 to Campbell; U.S. Ser. No. 08/842,660, filed Apr. 15, 1997, by J. Yan; and U.S. Ser. No. 08/837,993, filed Apr. 15, 1997, by J. Yan.
Aside from coated stents, there have been developments in the field of multilayer grafts. An example of a multilayer graft is disclosed in U.S. Pat. No. 4,743,252 to Martin, Jr. et al. Martin et al. shows a composite graft having a porous wall structure to permit ingrowth, which graft includes a generally nonporous, polymeric membrane in the wall to prevent substantial fluid passage therethrough so as to provide an implantable porous graft that does not require preclotting prior to implantation. Grafts are known which have multiple layers for strength reinforcement. For example, U.S. Pat. No. 5,282,860 to Matsuno et al. discloses a stent tube comprising an inner tube and an outer polyethylene tube with a reinforcing braided member fitted between the inner tube and the outer tube. The inner tube is made of a fluorine-based resin.
U.S. Pat. No. 5,084,065 to Weldon et al. discloses a reinforced graft assembly made from a vascular graft component and a reinforcing sleeve component. The reinforcing sleeve component may include one or more layers. The second component of the two component system includes the reinforcing sleeve component. Like the graft component, the reinforcing component includes a porous surface and a porous subsurface. Specifically, the reinforcing sleeve component includes multiple layers formed from synthetic, biologic, or biosynthetic and generally biocompatible materials. These materials are typically biocompatible polyurethane or similar polymers.
Despite progress in the art, there is presently no stent available that has a metallic cladding for improved strength reinforcement, expansion characteristics and radiopacity. Therefore, there is a need for such a multilayer metallic clad or laminate stent.